King Christian IX of Denmark signs the November constitution that declares Schleswig to be part of Denmark. This is seen by the German Confederation as a violation of the London Protocol and leads to the German–Danish war of 1864.

Christian IX was King of Denmark from 15 November 1863 until his death in 1906. From 1863 to 1864, he was concurrently Duke of Schleswig, Holstein and Lauenburg.

The history of Schleswig-Holstein consists of the corpus of facts since the pre-history times until the modern establishing of the Schleswig-Holstein state.

The Duchy of Schleswig was a duchy in Southern Jutland covering the area between about 60 km north and 70 km (45 mi) south of the current border between Germany and Denmark. The territory has been divided between the two countries since 1920, with Northern Schleswig in Denmark and Southern Schleswig in Germany. The region is also called Sleswick in English.

The German Confederation was an association of 39 predominantly German-speaking sovereign states in Central Europe. It was created by the Congress of Vienna in 1815 as a replacement of the former Holy Roman Empire, which had been dissolved in 1806 as a result of the Napoleonic Wars.

On 8 May 1852, after the First War of Schleswig, an agreement called the London Protocol was signed. This international treaty was the revision of an earlier protocol, which had been ratified on 2 August 1850, by the major German powers of Austria and Prussia. The second London Protocol was recognised by the five major European powers—Austria, France, Prussia, Russia, and the United Kingdom—as well as by the Baltic Sea powers of Denmark and Sweden.